Interaction between warfarin and erythromycin

In the patient described, marked exacerbation of the hypoprothrombinemic response to warfarin coincided with the addition of erythromycin to the drug regimen. A subsequent study in rats provided evidence that erythromycin is capable of increasing the anticoagulant response to single doses of warfarin. On the basis of case findings, preliminary laboratory data, and related clinical data we conclude that the interaction between warfarin and erythromycin is one of potential significance.